After the An Lushan Rebellion of the mid-8th century, the Tang Dynasty fell into gradual decline from the pinnacle of prosperity achieved just prior to that event. In response to mounting fiscal problems, the post-Rebellion emperors implemented various plans aimed at increasing government revenue. One of these plans envisioned “tribute” (jinfeng 進奉) from the provinces to be an important source of revenue, which upon receipt would be stored in the emperor’s treasury (originally the Neiku 内庫 [household treasury], later the Zuocangku 左蔵庫 [Finance Ministry treasury] and finally the Yanziku 延資庫 [banking treasury]. The present paper discusses the treasury known as the Yanziku.During the 9th century, the Tang Dynasty deployed troops, Fangqiu Bing 防秋兵, to guard the border areas of the northwest and southwest for which recruits were allotted from Bian forces (辺軍), Guandong forces (関東軍), and Shence forces (神策軍); and a border defense fund, Beibianku (備辺庫), was set up in order to finance the frontier military operations.This fund was the predecessor of the Yanziku, whose sources of revenue were tax money collected by fiscal, household registration and salt/iron functionaries, as well as tribute from the provinces earmarked for military aid.Due to the fact that the military aid revenue constituted tribute, it was in principle to be stored in the imperial household treasury (Neiku). However, since in fact the funds were transferred to the Yanziku under the supervision of the chancellor, the Yanziku came to take on the character of both a public and an imperial household treasury. This transfer also meant a reduction in the revenues managed by the imperial eunuchs and a significant, if only temporary, political victory for the chancellor and the bureaucracy.That is to say, the establishment of the Yanziku as a border defense fund at the same time enabled the bureaucracy to set up as a repository for military tribute that should have in principle been stored in the Neiku, and therefore was its first attempt to wrest fiscal authority away from the eunuchs. Although some success along these lines was achieved during the reign of Emperor Xuanzong, attempts to completely deprive the eunuchs of their control over public finance were never fully realized. Due to the continued failure of the Tang Dynasty to balance its fiscal budget, the Yanziku, which depended heavily on allocations of state revenues, was destined to also fall into decline.